Does this link work for you?
http://us.hardware.info/comparisontable/products/219130-215518-264808-216681
If not, it's a comparison between the 4, and assuming the Z97-Pro with WiFi is otherwise the same as the one without WiFi, I'd go Z97-Pro. The reason is the 12 phase CPU power, whereas the others are 8. The Maximus and Gamer offer a few more PCIe lanes, but if you're just going to put a GTX970 in there then all you need is a PCIe 3.0 x16 lane and honestly, every board can do that, even an ITX form factor. They are all similar with SATA, though this has a few more ports, and they're similar with USB 3.0 though this has a few more as well. Performance wise there's little variation, this is better in some benchmarks and the Maximus is better in others. It also has more PCIe x1 lanes, and no legacy PCI slots (finally).
I would avoid the Z97-A, not that it's not a good board but because it has an older sound chip. If you're using onboard then you'll get a better performance sound chip with any of the others, as they all use the same one. The Z97-A has a 15dB more noise than the others.
My next choice would be Maximus. The rest all have 8 CPU power phases, but this at least has no PCI slots, more PCIe x1 slots, and more SATA III ports than the Z97-A and Z97-Pro Gamer.